The listing or discussion of an apparently prior-published document in this specification should not necessarily be taken as an acknowledgement that the document is part of the state of the art or is common general knowledge.
The present invention is directed to a process to produce ester polyol esters (EPE) using renewable resources such as oils and fats, fatty acids, and fatty acid esters derived from plant and animal resources. These ester polyol esters are classified as Group V synthetic lubricant base stock and are particularly useful for use in high performance lubricant applications.
Group V lubricant base stocks include ester compounds and one type of high performance esters are polyol esters (PE) which are prepared by complete esterification of polyols such as TMP with monoacids. TMP trioleate is a common polyol ester formed from the esterification of the polyol TMP with oleic acid. Although Group V lubricant base stock technologies have demonstrated several performance advantages over traditional mineral oils, there is still room for further advancement or improvement in this field, especially with respect to enhancing performance characteristics of base stocks to extend the lubricant drain interval in high performance lubricant applications.
One of the common disadvantages of the commercially available polyol esters is related to high pour points, especially polyol esters produced from saturated fatty acids derived from tropical resources such as palm or coconut. Another disadvantage limiting performance is associated with the level of unsaturation where the double bonds in fatty acid components of polyol esters provide a point of attack for oxidation reactions to take place, which encourages oil degradation and precludes them for use in certain lubricant applications.
WO 2010/078505 discusses the preparation of ester polyols where the fatty acids derived from vegetable and/or animal oils are initially subjected to oxidative cleavage using ozone as the preferred cleavage reagent so that all double bonds are cleaved in a manner to generate carboxylic acid groups at each original double bonded carbon atom. In the oxidative ozonolysis of fatty acids derived from either vegetable oils or animal fats, a mixture of diacids and monoacids (referred to as ozone acids) are produced. The ozone acids are then esterified with select primary polyols such as TMP and/or other primary polyols to produce a wide range of polyol esters having a certain range of molecular weight and hydroxyl values.
In U.S. Pre-Grant Publication No. 2005/0112267, Yeong et al. concluded that common palm-based materials, especially palm olein or their ester derivatives developed for hydraulic application are only suitable for use in a tropical climate with temperatures ranging from 15° C. to 40° C. due to their low pour point.
The paper “Preparation and Characterization of Trimethylolpropane Esters from Palm Kernel Oil Methyl Esters” (Robiah et al., Journal of Oil Palm Research, 15(2), December 2003, pp. 42-49) reported that a lubricant base stock, i.e., TMP esters having an improved pour point in the range of 1° C. had been prepared from palm oil methyl ester (POME) and palm kernel oil methyl ester (PKOME). This improvement reflects that lubricant formulated with such esters can be used at a much lower temperature condition than reported previously. Malaysian Patent No. 140833 also filed by Robiah et al. discusses that the pour point of the TMP esters for the lubricant application can be reduced to a level of around −35° C. by removing via fractionation some of the saturated components in the ester mix. However, this separation step does not adequately remove all of the saturates to meet the most stringent requirement for pour point accepted by industry or original equipment manufacturers (OEMs).